Mold for casting metals



Patented Dec. 26, 1950 MOLD FOR CASTING METALS Robert D. Ahles, Schenectady, N. Y., assignor to General Electric New York Company, a corporation of No Drawing. Application March 10, 1948, Serial No. 14,161

2 Claims. 1

The present invention relates to the casting of metal and is particularly concerned with an improved mold. While the invention can be employed in the casting of any metal part, it is particularly concerned with the casting of high temperature alloys.

In the casting of various parts such as turbine buckets a number of conditions are encountered which require practices other than those normally used. For example, such castings must be held rather close to predetermined dimensions and there must be obtained cast products with sharp configurations and smooth surfaces free from surface imperfections. Previously many parts of this nature have been precision cast by what is known as the lost wax method and which comprises coating a wax form with a surface coating of finely divided refractory material, investing the coated .form in a suitable investment material and subsequently melting out the wax to complete the preparation of a mold having smooth, accurate walls. This process while having the disadvantage of being rather expensive has been rather widely employed for casting turbine buckets and the like due to the fact that parts of intricate or complicated shape, for example parts having relatively long narrow or thin portions, could be obtained free of surface or other imperfections. The present invention has as its primary object the provision of a mold which can be employed for casting metals, particularly high temperature alloys, without resort to wax forms and by means of which the dimensions of the cast productscan be held within rather narrow limits and there can be obtained smooth sharply defined surfaces requiring no further finishing other than the elimination of gate material. Another object of the invention is to provide a mold material which can be employed in the casting of metals within close dimensional tolerances without the need for a mold wash or lining.

The above objects are attained in accordance with the present invention by providing a mold consisting of a mixture of zirconite flour and linseed oil in the proportions of .4 to .5, preferably about .45 quart of linseed oil for each 15 pounds zirconite flour. The zirconite, i. e., zirconium silicate, employed in the practice of the invention should be a finely divided material at least 98 per cent of which will pass through a 325 mesh screen.

The zirconite flour and linseed oil are mixed in the usual manner and the resulting mixture rammed and baked following conventional procedures. The baked cores or molds are highly refractory, very dense, and very resistant to the penetration of the cast metal. Metal parts centrifugally or pressure cast in the molds of the present invention have excellent surface finishes, the cast products in general being characterized by a fine grain structure comparable to that of most wrought materials probably due to the good heat conductivity of the mold. Excellent tolerances can be obtained by the use of the molds of the present invention and it is unnecessary to employ any core or mold wash. While the materials employed are on the whole more expensive than normal sand mixes the total cost per mold compares favorably because of the decrease in labor required in rehandling and spraying regular cores. The used material can be reclaimed on a production basis. In preparing the zirconite flour-linseed oil compositions, it is essential that pure or substantially pure linseed oil be employed in the proportions indicated hereinbefore. The mixture of zirconite and linseed oil in the prescribed proportions have been found superior to mixtures in which part of the linseed oil has been replaced by a commercial core oil or part of the zirconite flour with flint or sand.

By use of the straight zirconite flour-linseed oil compositions smooth surface castings which can be held without trouble to a i .01 inch on small castings can readily be obtained. The resultant castings are also characterized by small grain size. In general, the castings can be sand blasted and used without further surface finishing.

While the invention is applicable to molds for the casting of any metal parts, it is particularly useful in the centrifugal or pressure casting of the more refractory metals and alloys such as the cobalt base alloys employed in the manufacture of turbine buckets which are to be exposed to elevated temperatures.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A mold composition consisting of a mixture of zirconite flour and linseed oil in the proportion of from 0.4 to 0.5 quart linseed oil for each 15 pounds zirconite flour, said flour being of a particle size such that at least 98 percent thereof will pass through a 325 mesh screen.

2. A mold for centrifugal or pressure casting metals consisting of a baked mixture of zirconite flour and linseed oil in the proportions of from 0.4 to 0.5 quart linseed oil for each 15 pounds zircomte flour, said zirconlte flame being a, finely divided materim at least 98 percent of which will pass through a 325 mesh screen.

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REFERENCES CMED The following references are of record in the w file of this patent:

Number 4 UNITED STATES PA'IENTB Name Date Prinzler Jan. 28, 1896 Lowe Oct. 29, 1918 Elliot Nov. 19, 1918 Bensing Nov. 1, 1932 Wheeler Oct. 10, 1933 Snell May 15, 1934 Hake et a1. Dec. 8, 1942 Seastone June 22, 1943 Feagln et a May 18, 1948 

1. A MOLD COMPOSITION CONSISTING OF A MIXTURE OF ZIRCONITE FLOUR AND LINSEED OIL IN THE PROPORTION OF FROM 0.4 TO 0.5 QUART LINSEED OIL FOR EACH 15 POUNDS ZIRCONITE FLOUR, SAID FLOUR BEING OF A PARTICLE SIZE SUCH THAT LEAST 98 PERCENT THEREOF WILL PASS THROUGH A 325 MESH SCREEN. 